1. Field of the Invention
The present invention relates to a computer system, more particularly, to a computer system having a microprogram instruction surveillance configuration.
2. Description of the Related Art
In computer systems, generally, a plurality of microprogram instructions performed by corresponding microprograms are provided in addition to the corresponding macro instructions, such as a LOAD instruction or a STORE instruction. One of the microprogram instructions can be used as a single macro in programs, simplifying use thereof. Each microprogram instruction consists of a plurality of subinstructions (or microinstructions), and thus can provide a composite function which cannot be performed by a macro instruction. On the other hand, the operation thereof differs from that of a normal macro instruction. Accordingly, a special logic circuit effecting the microprogram, instructions each of the microinstructions, must be provided in the computer system.
Programmers do not have to understand the subinstructions or microinstructions forming each microprogram instruction and circuit functions of special logic circuits, such as special registers used for performing the microprogram since the microprogram or microinstructions are stored in a read-only memory (ROM) or provided by a firmware as single instructions without any program error. Accordingly, the computer system is not provided with surveillance (or monitor) functions, for example, for directly accessing internal registers in the special logic circuit, temporary stopping the subinstructions (microinstructions), or tracing or tracking the subinstructions or microinstructions.
However, users may frequently suffer from trouble with the microprogram due to initial faults in the circuits performing the microprogram, external noise, program bugs, etc. In the case of such trouble, it is possible to run a hardware test, however, this is normally not very efficient and is limited to analyzing such trouble.
Other trouble with the microprogram may arise due to illegal use of the micro-microinstructions, for example, an illegal parameter set. Such trouble cannot be effectively solved by a hardware test.
Japanese Unexamined Patent Publication No. 58-195252 discloses a microprogram control apparatus for stopping the operation of a subinstructions or microinstruction during the execution of a microprogram when an address of the subinstructions or microprograms coincides with a set address to be stopped. The control apparatus stops the generation of a clock pulse. Accordingly, there may be trouble in the restart operation. The control apparatus also lacks surveillance functions for analyzing trouble quickly and efficiently.